Formation age and provenance of the Iman Group in the Khanka Massif: Evidence from U-Pb geochronology of detrital and magmatic zircons

In this paper, we present the zircon LA-ICP-MS U-Pb ages and Hf isotope compositions of detrital and magmatic zircons from the metasedimentary rocks and intrusive rocks within the Iman Group in the southern Khanka Massif to constrain the formation age and provenance of the Iman Group, and discuss the genesis and tectonic background of the intrusive muscovite monzogranites. The zircons separated from two-mica quartz schist in the Iman Group are euhedral-subhedral in shape, and display magmatic growth zones in their CL images, implying their magmatic origin. The dating results indicate that the 100 analytical spots over the detrital zirons yield a range of ages of 555 similar to 1322Ma. The main age populations are 555Ma, 612Ma, 700Ma, 739Ma, 769Ma, 839Ma and 936Ma. Their epsilon(Hf)( t) values and two-stage model ages (t(Dm2)) of 533Ma vary from - 4. 1 to +3 and from 1305Ma to 1755Ma, respectively. Their epsilon(Hf)( t) values and two-stage model ages (t(DM2)) of 700 similar to 839Ma vary from -3. 7 to +7. 8 and from 1246Ma to 1907Ma, respectively. The zircons from the muscovite monzogranite that intruded into the Iman Group yield a weighted mean Pb-206/ U-238 age of 443 +/- 3 Ma, its epsilon(Hf)( t) values and two-stage model ages (t(DM2)) range from -17. 6 to -4. 2 and 1688Ma to 2529Ma, respectively. Combined with the youngest age of the two-mica quartz schist and the formation time of the intruding muscovite monzogranite in the Iman Group, we conclude that the Iman Group was formed between 443 similar to 555Ma, i. e. , the Late Neo-Proterozoic to Late Ordovician. The age populations of the two-mica quartz schist, together with the regional magmatic events, indicate that the provenance of the Iman Group mainly come from the Neo-Proterozoic igneous rocks in the Songnen and Jiamusi massifs. Additionally, the muscovite monzogranites exhibit a geochemical affinity to adakitic rock, suggesting that its primary magma could be derived from partial melting of a thickened lower crustal material, which implies that the continental crust thickening might occur in the study area in the Late Ordovician.